A steam turbine is used so as to drive a machine or the like, and includes a turbine main body having a rotor which is rotatably supported. The rotor is rotationally driven by supplying steam serving as a working fluid to the turbine main body. Steam supplied to the turbine main body or steam extracted from the turbine main body flows through a steam channel of the steam turbine. A governing valve is provided in the steam channel. By adjusting an opening degree of the governing valve, it is possible to adjust a flow rate of the steam supplied to the turbine main body.
The governing valve is driven by an governing valve drive device. For example, PTL 1 discloses a governing valve drive device which includes an electric motor, and a switching mechanism such as a ball screw or the like which converts a rotary motion of the electric motor into a linear motion of a governing valve.
Since the ball screw includes a meshing portion having a contact angle in a spiral screw groove, if opening and closing operations of the governing valve are repeated for a long period, there is a problem that only a specific portion of the meshing portion of the ball screw is abraded.
PTL 2 discloses a configuration in which grease is supplied to a ball screw nut, into which a ball screw shaft having screw grooves formed on the outer circumference surface is screwed, from the outside.
PTL 3 disclose a configuration in which a ball screw is accommodated in a tubular housing and a grease supply pipeline for supplying grease to a ball screw nut screwed into a ball screw shaft from the outside is provided. In this configuration, the grease supply pipeline is provided inside a stator of an electric motor for rotationally driving the ball screw and integrally rotates with a rotor.